The invention relates to a thermal test pattern for a collimator. The test pattern can be used to check the operation of an infrared camera.
The resolving power of a camera is determined by a test pattern by establishing the number of observed stripes per surface unit. When this determination is carried out in the laboratory, the test pattern consists of a number of slots provided in a metal screen. The observed slots have a temperature which is equal to that of a black body which is placed behind the screen. The temperature difference between the black body and the screen is accurately determined. If it is desired to establish the performance limits of the camera, collimators having large dimensions can be used.
If, however, the thermal camera is mounted on board of an airplane, for example, it is not possible to have the extensive measuring equipment for carrying out tests of the video circuit. In that case, only a single control operation can be performed, and it must be performed rapidly and at any instant, even if the surroundings observed by the camera do not exhibit any thermal gradient. This is the case, for example, during a flight over the sea where the picture is nearly uniform when no ship or other object is visible. Under these circumstances, the camera can be tested by using a collimator of smaller dimensions which forms a thermal test pattern at infinity. The test pattern is recorded by the camera mounted in a gyrostabilized tower. The camera is directed so that its axis is parallel to the collimator's axis.